Bar graphs showing the mean (equal to least squares means) and standard error (error bars) for different measures of song in typical (light gray) and purring (dark gray) male T. oceanicus. A. Peak frequency of airborne acoustic signals recorded with a microphone; B. Linear amplitude of airborne acoustic signals recorded with a microphone. C. Peak frequency of substrate-borne vibrations recorded with an accelerometer; D. Linear amplitude of substrate-borne vibrations recorded with an accelerometer. The asterisk indicates p<0.001. Effect sizes (Cohen’s D) are as follows: A. 1.83, B. 4.46, C. 1.05, and D. 0.27.